Enhanced synthesis of racemic metallocenes

ABSTRACT

Chiral metallocenes are prepared by reacting a salt of an asymmetric bis(cyclopentadienyl) moiety containing ligand with a chelate diamine adduct of a transition, lanthanide, or actinide metal halide in an organic solvent medium so as to produce said chiral metallocene.

This application is a continuation-in-part of application Ser. No.08/427,505, filed Apr. 24, 1995, now U.S. Pat. No. 5,556,997, issuedSep. 17, 1996.

The invention relates generally to the preparation of metallocenes whichare useful as stereoregular oiefin polymerization catalysts and morespecifically to a process for metallizing cyclopentadienyl ligand saltswith certain transition, lanthanide or actinide metal compounds whichare chelate diamine adducts of the metal halides.

As known in the art, metallocenes can be prepared by reacting a metalcompound of the formula MX_(n), where M is the metal, n is an integer of1 to 6, depending upon the valence of M, and X is independently ananionic ligand group or a neutral Lewis base ligand group having up to30 non-hydrogen atoms such as hydride, halo, alkyl, aryl, silyl, germyl,aryloxy, aikoxy, amide, and siloxy, with an alkali metal or a magnesiumhalide salt of a cyclopentadienyl ligand in a solvent such as an ether.

Chiral metallocenes are useful for the synthesis of polyolefins.Specifically, the racemic form of the metallocene provides stereoregularpoly(alpha-olefins) in addition to being considerably more active thanthe meso form, which produces only atactic polymers. An efficientsynthesis of chiral metallocenes that favors the formation of theracemic isomer at the metallation stage is desired. We have now foundthat by using certain chelate diamine adducts of a metal halide in thereaction with the salt of the cyclopentadienyl ligand, enhancedformation of the racemic isomer and/or better product yields can beproduced, especially by using a mixed ether-hydrocarbon reaction solventmedium and/or by preparing the adduct at elevated temperatures.

In accordance with this invention there is provided a process forpreparing a chiral metallocene, said process comprising reacting a saltof an asymmetric bis(cyclopentadienyl) moiety containing ligand with achelate diamine adduct of a transition, lanthanide or actinide metalhalide in an organic solvent medium so as to produce said chiralmetallocene.

Chiral metallocenes which can be prepared in accordance with the processof the invention preferably contain a metal from Groups 3-10, or thelanthanide and actinide series of the Periodic Table of the elementsand, more preferably a Group 4 to 6 transition metal, which iscoordinated with a ligand containing a pair of cyclopentadienylmoieties, at least one of which is asymmetric, which moieties arestereorigid such as by being joined by a bridging group. Thecyclopentadienyl moieties can be substituted with one or more groups,such as halogen, amino, mercapto, phosphino, and C₁ to C₂₀ hydrocarbyl,silahydrocarbyl, or halohydrocarbyl and the like and can includemoieties which are condensed, multi-ring structures such as, forexample, indenyl, benzoindenyl, or fluorenyl, which structures can behydrogenated and/or further substituted. The other groups on the metalatom usually include hydride, halogen, hydrocarbyl or halohydrocarbylhaving up to about 6 carbons. Such chiral metallocenes, and their use ascatalysts in forming isotactic olefin polymers are described, forexample, in U.S. Pat. Nos. 5,017,714; 5,036,034; 5,145,819; 5,296,434;5,324,800 and 5,329,033, whose disclosures are incorporated herein byreference. Typical bridging groups include silicon containing bridges of1-4 atoms selected from silanylene, silaalkylene, oxasilanylene andoxasilaalkylene, such as, dimethylsilanylene. The chiral metallocenesare mixtures of racemic diasteriomers which have no plane of symmetry.In contrast, the meso isomers have a plane of symmetry running throughthe metal between the rings and are, therefore achiral.

Specific, non-limiting examples of chiral metallocenes include racemic:

1,1'-dimethylsilanylene-bis(3-methylcyclopentadienyl)!zirconiumdichloride;

1,1'-dimethylsilanylene-bis(indenyl)!zirconium dichloride;

1,1'-dimethylsilanylene-bis(4,5,6,7-tetrahydroindenyl)!zirconiumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-methylcyclopentadienyl)!zirconiumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!zirconiumdichloride;

1,1'-dimethylsilanylene-bis(3-trimethylsilanylcyclopentadienyl)!zirconiumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-trimethylsilanylcyclopentadienyl)!zirconiumdichloride;

1,1'-(1,1,3,3-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!zirconiumdichloride;

1,1'-(1,1,4,4-tetramethyl-1,4-disiianylbutylene)-bis(4,5,6,7-tetrahydroindenyl)!zirconiumdichioride;

1,1'-(2,2-dimethyl-2-silaprooylene)-bis(3-methylcyclopentadienyl)!zirconiumdichloride;

1,1'-dimethylsilanylene-bis(3-methylcyclopentadienyl)!titaniumdichloride;

1,1'-dimethylsilanylene-bis(indenyl)!titanium dichloride;

1,1'-dimethylsilanylene-bis(4,5,6,7-tetrahydroindenyl)!titaniumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-methylcyclopentadienyl)!titaniumdichoride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!titaniumdichoride;

1,1'-dimethylsilanylene-bis(3-trimethylsilanylcyciopentadienyl)!titaniumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-trimethylsilanylcyclopentadienyl)!titaniumdichloride;

1,1'-(1,1,3,3-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!titaniumdichioride;

1,1'-(1,1,4,4-tetramethyl-1,4-disilanylbutylene)-bis(4,5,6,7-tetrahydroindenyl)!titaniumdichioride;

1,1'-(2,2-dimethyl-2-silapropylene)-bis(3-methylcyciopentadienyl)!titaniumdichloride;

1,1'-dimethylsilanylene-bis(3-methylcyciopentadienyl)!hafniumdichloride;

1,1'-dimethylsilanylene-bis(indenyl)!hafnium dichloride;

1,1'-dimethylsilanylene-bis(4,5,6,7-tetrahydroindenyl)!hafniumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-methylcyclopentadienyl)!hafniumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!hafniumdichloride;

1,1'-dimethylsilanylene-bis(3-trimethylsilanylcyclopentadienyl)!hafniumdichloride;

1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-trimethylsilanylcyclopentadienyl)!hafniumdichloride;

1,1'-(1,1,3,3-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)!hafniumdichloride;

1,1'-(1,1,4,4-tetramethyl-1,4-disilanylbutylene)-bis(4,5,6,7-tetrahydroindenyl)!hafniumdichloride;

1,1'-(2,2-dimethyl-2-silapropylene)-bis(3-methylcyclopentadienyl)!hafniumdichioride;

dimethylsilylbis(1-(2-methyl-4-ethylindenyl))zirconium dichloride;

dimethylsilylbis(1-(2-methyl-4-isopropylindenyl))zirconium dichloride;

dimethylsilylbis(1-(2-methyl-4-tert-butylindenyl))zirconium dichloride;

methylphenylsilylbis(1-(2-methyl4-isopropylindenyl))zirconiumdichloride;

dimethylsilylbis(1-(2-ethyl-4-methylindenyl))zirconium dichioride;

dimethylsilylbis(1-(2,4-dimethylindenyl))zirconium dichloride;

dimethylsilylbis(1-(2-methyl-4-ethylindenyl))zirconium dimethyl;

dimethylsilyl(2-methyl-4,5,6,7-tetrahydro-1-indenyl)₂ zirconiumdichloride;

ethylene(2-methyl4,5,6,7-tetrahydro-1-indenyl)₂ zirconium dichloride;

dimethylsilyl(2-methyl-4,5,6,7-tetrahydro-1-indenyl)₂ dimethylzirconium;

phenyl(methyl)silyl(indenyl)₂ zirconium dichloride;

dimethylsilyl (2,3,5-trimethyl-1-cyciopentadienyl)₂ zirconiumdichloride;

dimethylgermyl(indenyl)₂ zirconium dichloride;

ethylene(indenyl)₂ zirconium dichloride;

methylene(3-t-butyl-1-cyclopentadienyl)₂ zirconium dichloride;

dimethylsilyl(4,7-dimethyl-1-indenyl)₂ zirconium dichloride;

dimethylsilanyl-bis(indenyl)thorium dichloride; and

dimethylsilanyl-bis(indenyl)uranium dichloride.

The metallocenes are prepared by first deprotonating the appropriateligand compound using an alkali metal, an alkali metal salt, a magnesiumsalt or a Grignard reagent to form an alkali metal, magnesium ormagnesium halide salt of the ligand. Examples of deprotonizing agentsinclude Na powder, RLi, NaH, LiH and RMgX, where R is C₁ to C₁₀hydrocarbyl and X is halogen. Preferred are alkyllithium compounds suchas methyllithium, n-butyllithium, s-butyllithium, t-butyllithium,phenyllithium and the like.

Suitable reaction solvents are aliphatic or aromatic hydrocarbon orhalocarbon solvents and acyclic or cyclic ethers. Mixed ether andhydrocarbon or halohydrocarbon solvents in ratios of from about 9:1 to1:9 by volume ether to hydrocarbon solvent and, preferably, 4:1 to 1:2provide improved yields of the metallocenes having increased racemicisomer content. Examples of suitable solvents include diethyl ether,tetrahydrofuiran (THF), ethylene glycol dimethyl ether, hexanes,cyclohexane, heptane, pentane, toluene, benzene, xylene, chlorobenzeneand the like. Mixtures of THF and toluene are preferred to provideenhanced yields of racemic isomer enriched product.

The ligand salt, such as the dilithium salt, from the deprotonation isreacted with a chelate diamine adduct of a transition, lanthanide oractinide metal compound and, preferably a metal halide, in order to formthe racemic metallocene. Suitable diamines for forming the adducts whichare effective to provide metallocenes with an enhanced yield of racemicisomer, include tertiary diamines and especiallyN,N,N'N'-tetramethylethylenediarnine (TMEDA) andtetramethyldiaminomethane (TMDAM). A metal chloride to diamine ratio of1:0.5 to 1:5 provides improved yields of the racemic metallocene. Aboutequimoiar to about a 10% excess of diamine is preferably used.Preferably, the diamine adduct of the metal is formed prior to mixing itwith the ligand.

Non-limiting examples of transition, lanthanide and actinide metalsinclude Ti, Zr, Hf, V, Cr, La, Ce, Th, U and the like. Preferred forcatalyst use are the Group 4 metals Ti, Zr and Hf.

The adducts can be prepared in hydrocarbon solvents such as those namedabove for the deprotonation reaction and, preferably toluene, and eitherseparated from the solvent, such as by filtration, or the adduct insolvent can be used in situ for metallation.

It has been found that the yields of metallocene product are improved bypreparing the adduct at elevated temperature, e.g. about 40° to 110° C.NMR indicates that the composition of the adduct is different ascompared with adducts prepared at ambient temperatures.

It was found that in carrying out the metallation reaction, a mixedhydrocarbon/ether solvent (toluene/THF) reaction medium gave higheryields of enhanced rac/meso isomer ratio product. The metallationreaction temperature is not critical and can range from about -20° to120° C. and, preferably, from about 0° to 600° C. Stoichiometric toabout a 10% excess amount of metal adduct to ligand salt is preferablyused. It was also found that adding a small amount of metalloceneproduct (preferably, amounts which are about 0.05 to 5 wt. % of themetal adduct) and/or ether solvent (THF) (preferably amounts which areabout 1 to 20 wt. % based on total solvent) to the adduct slurry priorto the metallation reaction further enhances yields and reproducabilitywhich lowers costs by reducing the cycle time. The filterability of theproduct mixture also improved and can be further enhanced by adding anon-polar solvent such as a paraffin (hexane) to the solution.

The invention is further illustrated by, but is not intended to belimited to, the following examples.

EXAMPLE 1a

ZrCl₄ (61.9 grams, 0.266 mol) was slurried in 400 mL of anhydroustoluene. N,N,N',N'-Tetramethylethylenediamine (TMEDA) (31.74 grams,0.273 mol) was added dropwise over 20 minutes. The slurry was stirredovernight and then filtered on a coarse frit. The solids were washedwith 50 mL of toluene and dried in vacuo. The yield of Zrcl₄ (TMEDA) was88.2 grams (95%).

EXAMPLE 1b

ZrCl₄ (TMEDA) (35.56 g; 0.102 mol) from Example 1a was placed in a 1 Lflask with 260 mL of THF. Most of the solids dissolved. After coolingthis material to 0° C. a THF solution of dilithium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (40.93 grams, 0.102 mol; 300 mLTHF) was added dropwise over 3.5 hours. An orange solid precipitated.The reaction was warmed to ambient temperature and stirred overnight.The orange solids were then filtered on a coarse frit, washed with 25 mLof THF, and dried in vacuo. The yield of crudedimethylsilyl-bis(2-methylindenyl)zirconium dichloride product was 12.24grams (26%). This solid was extracted with 700 mL of methylene chloride,filtered through a medium frit, and stripped nearly to dryness. Hexaneswere added (100 mL) to precipitate the dissolved product. Therecrystallized product was filtered on a coarse frit. The purified yieldwas 8.59 grams (18%). ¹ H NMR in CDCl3 revealed a pure product composedof 93% racemic and 7% meso diasteriomers.

EXAMPLE 2

ZrCl₄ (2.26 grams, 0.00970 mol) was slurried in 20 mL of anhydroustoluene. TMEDA (1.23 g, 0.0106 mol) was added dropwise. The slurry wasstirred for 17 hours. Dilithium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (3.87 grams, 0.00961 mol) wasdissolved in 27 mL of anhydrous THF and added dropwise to the zirconiumslurry over approximately ten minutes. The solution cleared brieflyduring the addition and then an orange solid precipitated. The reactionwas stirred overnight. The orange solids were then filtered on a mediumfrit, washed with 10 mL of toluene, and dried in vacuo. The yield ofcrude dimethylsilyl-bis(2-methylindenyl)zirconium dichloride product was2.75 grams (60%). After extracting this material into methylenechloride, the purified yield was determined to be 55%. A ¹ H NMRspectrum in CDCl3 showed pure product composed of 93% racemic and 7%meso diasteriomers of dimethylsilylbis(2-methylindenyl)zirconiumdichloride product.

EXAMPLE 3

ZrCl₄ (2.24 grams, 0.00961 mol) was slurried in 20 mL of anhydroustoluene. TMEDA (1.23 grams, 0.0106 mol was added dropwise. After lessthan five minutes, dilithium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (3.86 grams, 0.00959 mol) in 27mL of anhydrous THF was added dropwise to the zirconium slurry overapproximately fifteen minutes. The solution cleared briefly during theaddition and then an orange solid precipitated. The reaction was stirredovernight. The orange solids were then filtered on a medium frit, washedwith 10 mL of toluene, and dried in vacuo. The yield of crudedimethylsilyl-bis(2-methylindenyl)zirconium dichloride product was 2.51grams (55%). After extracting this material into methylene chloride, thepurified yield was determined to be 47.5%. A ¹ H NMR spectrum in CDCl3showed pure product composed of 93% racemic and 7% meso diasteriomers.

EXAMPLE 4

ZrCl₄ (2.95 grams, 0.0127 mol) was slurried in 30 mL of anhydroustoluene. Tetramethyldiarminomethane (TMDAM) (1.42 grams, 0.00139 mol)was added dropwise to the slurry. The slurry was stirred overnight.Dilithium salt of dimethylsilyl-bis(2-methylindene) (Et₂ O) (5.112grams, 0.0127 mol) dissolved in 35 mL of anhydrous THF was addeddropwise to the zirconium slurry at ambient temperature. The solutioncleared briefly during the addition and then an orange solidprecipitated. The reaction was stirred overnight. The orange solids wereisolated on a coarse frit, washed with toluene, and dried in vacuo. Theyield of crude dimethylsilyl-bis(2-methylindenyl)zirconium dichlorideproduct was 3.43 grams (57%). A ¹ H NMR in CDCl3 showed the product tobe of similar purity to the crude product of Example 2.

COMPARISON EXAMPLE 1

ZrCl₄ (THF)₂ (2.17 g; 0.00575 mol) was placed in a 100 mL Schmenk flaskwith 15 mL of anhydrous THF. A portion of the solids dissolved. Aftercooling this material to 0° C., a THF solution of dilithium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (2.32 grams, 0.00576 mol; 17 mLTHF) was added dropwise over 25 minutes. A dark orange solutionresulted. No solids precipitated. The reaction was warmed to ambienttemperature and stirred overnight. An aliquot of the clear solution wasthen stripped to an oily solid and redissolved in THF-d₈ for ¹ H NMR.The NMR spectrum showed little or no racemic product.

COMPARISON EXAMPLE 2

ZrCl₄ (THF)₂ (2.17 g; 0.00575 mol) was placed in a 100 mL Schienk flaskwith 13 mL of anhydrous toluene. This slurry was stirred with a magneticstir bar and a solution of dilitnium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (2.32 grams, 0.00576 mol) in 16mL of THF was added dropwise over 11 minutes. The reaction went clearand the solution became a dark orange. Toward the end of the additionthe solution clouded and a precipate began to form. The reaction wasstirred overnight. The orange solids were then filtered on a 30 mLmedium frit, washed with several mLs of toluene, and dried in vacuo. Theyield of orange and brown solids was 1.03 grams (37.5%). Afterextracting this material into methylene chloride, the purified yield wasdetermined to be 23%. A ¹ H NMR spectrum in CDCl₃ showed pure productcomposed of approximately 93% racemic and 7% meso diasteriomers ofdimethylsilyl-bis(2-methylindenyl)zirconium dichloride.

EXAMPLE 5

ZrCl₄ (1.58 grams, 0.0678 moles) was slurried in 16 mL of anhydroustoluene. THF (1.17 grams, 0.0162 moles) was added dropwise. The droppingfunnel was then charged with a solution of dilithium salt ofdimethylsilyl-bis(2-methylindene)(Et₂ O) (2.74 grams, 0.00681 mol andTMEDA (0.81 grams, 0.00697 mol) in 19 mL of anhydrous THF. Afterstirring for two hours, the solution of the dilithium salt ofdimethylsilyl-bis(2-methylindene) (TMEDA) was added dropwise to thezirconium slurry. The solution cleared briefly during the addition andthen an orange solid precipitated. The reaction was stirred overnight.The orange solids were then filtered on a medium frit, washed with 8 mLof toluene, and dried in vacuo. The yield of crudedimethylsilyl-bis(2-methylindenyl)zirconium dichloride was 1.26 grams(39%). The crude material provided a typical ¹ H NMR spectrum in CDCl₃.The metailocene product was approximately 95% racemic and 5% meso. Apurified yield was not determined.

EXAMPLE 6

ZrCl₄ (3.04 grams, 0.0130 mol) was slurried in 13 mL of anhydroustoluene. TMEDA (1.57 grams, 0.0135 mol) was added dropwise. THF (8 mL)was then added. The slurry was stirred for 1.5 hours. The dilithium saltof dimethylsilyl-bisindene(Et₂ O) (4.85 grams, 0.0130 mol) was dissolvedin 28 mL of anhydrous THF and then added dropwise to the zirconiumslurry over 25 minutes. The solution cleared briefly during the additionand then an orange solid precipitated. The reaction was stirredovernight. The orange solids were then filtered on a coarse frit, washedwith 5 mL of toluene and 5 mL of hexanes, and dried in vacuo. The yieldof dimethylsilyl-bis(indenyl)zirconium dichloride was 4.44 grams (76%).A sample was dissolved in CDCl₃ for ¹ H NMR. The NMR spectrum showedpure racemic product.

COMPARISON EXAMPLE 3

ZrCl₄ (3.03 grams, 0.0130 mol) was slurried in 13 mL of anhydroustoluene. THF (8 mL) was then added. A dropping funnel was charged with asolution of the dilithium salt of dimethylsilyl-bisindene (Et₂ O) (4.85grams, 0.0130 mol) in 28 mL of anhydrous THF. After stirring for onehour, the ligand solution was added dropwise to the zirconium slurryover 30 minutes. The solution cleared briefly during the addition andthen, almost irnnediately, an orange solid precipitated. The reactionwas stirred overnight. The orange solids were then filtered on a coarsefrit, washed with 5 mL of toluene and 5 mL of hexanes, and dried invacuo. The yield of dimethylsilyl-bis(indenyl)zirconium dichioride was4.13 grams (71%). A sample was dissolved in CDCl₃ for ¹ H NMR. The NMRspectrum showed pure racemic product.

EXAMPLE 7

Under a N₂ pad, ZrCl₄ (2.56 grams, 0.011 mol), 18 grams toluene solventand TMEDA (1.32 grams, 0.0114 mol) in a 100 cc flask were stirred,heated up and held at 80°-90° C. for 1 hour. After cooling down, amixture of THF (1.0 gram), dimethylsilyl-bis(indenyl) zirconiumdichloride (0.04 gram), and toluene (4.0 grams) were added at 17° C. Thedilithium salt of dimethylsilyl-bisindene-(Et₂ O) (22.33 grams, 0.01mol) in THF solution (18 weight percent) in a dropping funnel was thenfed continuously with the first half being fed for 30 minutes and thesecond half for 55 minutes at 18°-23° C. The reaction mixture wasstirred at ˜23° C. for 25 hours and then moved to a dry box. Theresultant orange slurry was easily filtered (with a 60 cc 4-4.5 micronglass frit filter) and 7 grams of toluene were used to wash the wetcake. After being dried, 4.57 grams of orange product were obtained(˜94% crude yield excluding the added dimethlsilyl-bis(indenyl)zirconium dichioride) based on dilithium salt ofdimethylsilyl-bisindene-(Et₂ O). NMR showed that the sample of the crudeproduct had 88% racemic and 12% meso isomers.

Example 1 demonstrates that by using a diamine adduct in THF, racemicproduct was produced in contrast to Comparison Example 1 which producedlittle or no racemic product. Examples 2 to 6 demonstrate the improvedyields obtained by using a mixed solvent in combination with the diamineadduct.

Example 7 demonstrates that an improved yield of an easily filterableproduct is obtained by preparing the diamine adduct at elevatedtemperatures and adding a small amount of product and THF to the adductprior to the metallization reaction.

We claim:
 1. A process for preparing a chiral metallocene, said processcomprising:a) reacting at an elevated temperature a chelate diamine witha metal halide of a transition, lanthanide or actinide metal so as toproduce a chelate diamine adduct of said metal halide; and b) reactingin an organic solvent medium a salt of an asymmetricbis(cyclopentadienyl) moiety-containing ligand with chelate diamineadduct produced in a) so as to produce a chiral metallocene.
 2. Theprocess of claim 1 wherein said metal halide is a Group 4-6 metalhalide.
 3. The process of claim 1 wherein said organic solvent medium isa mixture of an ether and an aromatic hydrocarbon and said chiralmetallocene precipitates from said medium.
 4. The process of claim 3wherein said organic solvent medium is a mixture of tetrahydrofuran andtoluene.
 5. The process of claim 1 wherein said chelate diamine isselected from the group consisting N,N,N',N'-tetramethylethylenediamineand tetramethyldiaminomethane.
 6. The process of claim 1 wherein saidligand comprises a pair of cyclopentadienyl moieties, at least one ofwhich is asymmetric, which are joined by a silicon containing bridginggroup.
 7. The process of claim 6 wherein said bridging group contains1-4 atoms and is selected from the group consisting of silanylene,silaalkylene, oxasilanylene and oxasilaalkylene.
 8. The process of claim7 wherein said bridging group is dimethylsilanylene.
 9. The process ofclaim 7 wherein said chiral metallocene isracemic-dimethylsilyl-bis(2-methylindenyl)zirconium dichloride.
 10. Theprocess of claim 7 wherein said chiral metallocene is racemicdimethylsilyl-bis(indenyl)zirconium dichloride.
 11. The process of claim1 wherein said salt is an alkali metal salt or a magnesium halide salt.12. The process of claim 1 wherein said salt is an alkali metal salt ora magnesium halide salt of an asymmetric bis(cyclopentadienyl)moiety-containing ligand; wherein said metal halide is a Group 4 metalhalide; and wherein said solvent medium is a mixed ether-aromatichydrocarbon solvent medium.
 13. The process of claim 12 wherein thechelate diamine is N,N,N',N'-tetramethylethylenediamine ortetramethyldiaminomethane and said metal halide is zirconiumtetrachloride.
 14. The process of claim 13 wherein said salt is thedilithium salt of dimethylsilyl-bis(2-methylindene) and said chiralmetallocene is racemic-dimethylsilyl-bis(2-methylindenyl)zirconiumdichloride.
 15. The process of claim 1 wherein said temperature is fromabout 40° to 110° C.
 16. A process for preparing a chiral metallocene,said process comprising reacting a salt of an asymmetricbis(cyclopentadienyl) moiety-containing ligand with a chelate diamineadduct of a transition, lanthanide or actinide metal halide in anorganic solvent medium so as to produce a chiral metallocene, whereinchiral metallocene corresponding to chiral metallocene to be produced insaid process and/or tetrahydrofuran is added to said adduct prior toreacting said adduct with said salt.
 17. The process of claim 16 whereinat least said chiral metallocene corresponding to chiral metallocene tobe produced in said process is added.
 18. The process of claim 16wherein said metal halide is a Group 4-6 metal halide.
 19. The processof claim 16 wherein said organic solvent medium is a mixture of an etherand an aromatic hydrocarbon and chiral metallocene produced in saidprocess precipitates from said medium.
 20. The process of claim 19wherein said organic solvent medium is a mixture of tetrahydrofuran andtoluene.
 21. The process of claim 16 wherein said diamine adductcontains a diamine selected from the group consistingN,N,N',N'-tetramethylethylenediamine and tetramethyldiaminomethane. 22.The process of claim 16 wherein said ligand comprises a pair ofcyclopentadienyl moieties, at least one of which is asymmetric, whichare joined by a silicon containing bridging group.
 23. The process ofclaim 22 wherein said bridging group contains 1-4 atoms and is selectedfrom the group consisting of silanylene, silaalkylene, oxasilanylene andoxasilaalkylene.
 24. The process of claim 23 wherein said bridging groupis dimethylsilanylene.
 25. The process of claim 23 wherein said chiralmetallocene is racemic-dimethylsilylbis(2-methylindenyl)zirconiumdichloride.
 26. The process of claim 23 wherein said chiral metalloceneis racemic-dimethylsilylbis(indenyl)zirconium dichloride.
 27. Theprocess of claim 16 wherein said salt is an alkali metal salt or amagnesium halide salt.
 28. The process of claim 16 wherein said salt isan alkali metal salt or a magnesium halide salt of an asymmetricbis(cyclopentadienyl) moiety-containing ligand; wherein said metaladduct is a chelate diamine adduct of a Group 4 metal halide; andwherein said solvent medium is a mixed ether-aromatic hydrocarbonsolvent medium.
 29. The process of claim 28 wherein the chelate diamineadduct is an adduct of N,N,N',N'-tetramethylethylenediamine ortetramethyldiaminomethane and zirconium tetrachloride.
 30. The processof claim 29 wherein said salt is the dilithium salt ofdimethylsilylbis(2-methylindene) and said chiral metallocene isracemic-dimethylsilylbis(2-methylindenyl)zirconium dichloride.
 31. Theprocess of claim 16 wherein said adduct is prepared by reacting saiddiamine with said metal halide and an elevated temperature.
 32. Theprocess of claim 31 wherein said temperature is from about 40° to 110°C.